1. Field of the Invention
The present invention generally relates to a keypad assembly, and in particular, to a keypad assembly including a light guide plate.
2. Description of the Related Art
A conventional keypad assembly used in portable terminals generally includes a keypad and a switch board. The keypad includes an elastic layer in a plate form and a plurality of key buttons formed on a first surface of the elastic layer. The key buttons may have characters, numbers or symbols printed thereon. In the switch board, a plurality of switches is used to form electric contact by pressing a key button to convert the press of the key button into an electric signal.
Portable terminals may include an illumination means capable of emitting light. This allows for the use of a keypad even in a dark place. In the illumination means, a plurality of light emitting diodes are arranged on a printed circuit board (PCB) or an inorganic electro-luminescence material may be inserted into an elastic pad.
FIG. 1 illustrates the structure of a conventional keypad assembly. The conventional keypad assembly includes a pad 112, a key button 111 formed on the pad 112, a keypad 110 including a light guide plate 113 under the pad 112, a light source (not shown) for irradiating light from a side of the light guide plate 113 into the light guide plate 113, and a switch board 120.
The switch board 120 includes at least one dome switch 121 and a PCB 122 on whose surface the dome switch 121 is formed. An electric contact between the dome switch 121 and the PCB 122 can be formed by pressing the key button 111.
The keypad 110 may be combined with the key button 111 and the pad 112 may be integrated in one body or separately formed. The pad 112 may be made of rubber having elasticity to restore the key button 111 to its original state upon the release of the pressure applied by a user.
In the light guide plate 113, a pressing protrusion 113a is formed in a position corresponding to the dome switch 121. Reflective patterns 113b for reflecting a part of the light irradiated into the light guide plate 113 to the key button 111 are formed around the pressing protrusion 113a. A part of the light irradiated into the light guide plate 113 is reflected to the key button 111 by the reflective patterns 113b and the remaining of the light is irradiated from another side of the light guide plate 113.
However, the light irradiated from the side of the light guide plate 113 illuminates not only the key button 111 but other portions of the assembly as well. This causes loss of light and may distract the user's eyes from the key button 111.